This thesis presents a low-energy application specific digital controller for a battery-free 2.4 GHz wireless sensor network (WSN) node. The digital controller has been designed and fabricated in a standard 0.13 μm CMOS and implements a simple protocol for WSNs. Techniques such as supply voltage reduction and power gating have been implemented to provide an energy reduction of 50X over traditional microcontrollers and a 2X reduction compared to the Smart Dust processor. A silicon area of 0.85 mm² makes it easy to integrate the digital controller with the sensor and the transceiver. For a 2 MHz input clock frequency, the digital core consumes 5.4 pJ per instruction with a single 0.5 V supply.